1. Field of the Art
The present invention relates to computer subsystem communications, and, more particularly, to a method and apparatus for creating an extensible storage area network (SAN) architecture by interconnecting multiple storage router type devices—which may be viewed as the nodes in a framework which is the SAN—providing coupling of host computers to storage drive arrays or subsystems.
2. Description of the Related Art
Although most of the concepts of networked storage are rooted in technology that has existed for several decades, there are recent developments in computing which have lead to drastically increased demands for storage space. This is due in a large part to the advent of massive unstructured data flows, observed to stem from the mass acceptance of the internet and its related methods of communications and dissemination of information, as opposed to those associated with structured data flows, typical examples of which are Enterprise Resource Planning (ERP) systems, and Electronic Document Interchange (EDI) systems. There is a growing need to effectively control and manage data storage activities related to the former, the latter being more easily able to be controlled and managed. As such, new challenges are brought forth related to facilitating server and storage consolidation, non-disruptive back-up procedures, and minimizing the distance limitations of technologies preceding storage area networking.
This need has led to the development of what is commonly referred to as a ‘Storage Area Network’ (SAN). Within a SAN, host computers provide access to arrays of storage devices that can be either local or remotely located, and can be either centralized in one location or distributed over many. This variability and the complexity of such storage subsystems mandates that the host computers be coupled to devices that can route requests to the storage devices and make their actual configuration transparent to the end-user (e.g., ‘storage routers’). This added network (the SAN) between the hosts and the storage devices, when properly set up and configured by an administrator, releases the end-user from the need to be concerned with the actual physical layout of the storage.
Traditional approaches to storage and storage management emphasize the need to control expense and restrict access. Prior technology has generally only enabled a given storage device to be accessible to a single server, so the latter goal is managed with relative ease though apparently working against achieving the former where there is such a one-to-one ratio of dependency. While one cost factor, that of the physical hardware performing the storage role, has exponentially decreased over the time since the advent of computing as a viable business tool, the cost associated with management now has continued to increase at an increasing rate, offsetting any benefits the former brings.
The important function of managing storage in a networked environment has proven to be generally difficult, and when comparing the approaches of management through a server-provided interface with storage-specific direct connect-based management, a definite trend for success has been correlated with the latter. Just as data has been seen to come to be valued as an independent strategic asset from the computers that access it, storage networking products and architectures, as platforms for data protection and storage management are just now being elevated to the same level of concern.
To ensure reliability, redundant access is often supported, employing multiple routing devices, some of which may be distributed across geographically distant locations. Although a comparatively new technology, common existing implementations of SANs have to date been observed as failing in a critical area, that of not readily supporting extensibility. An essential characteristic for a SAN is that it must be scalable if it is to support the increasing rate of growth of demand for storage space.
It is therefore desirable to introduce greater simplicity into the hardware used to communicate between a host system and storage array, while meeting the prerequisites of redundancy and reliability (collectively termed as high availability). Preferably, a suitable SAN architecture also provides improved performance and reduces the running cost of the SAN, ideally maintaining transparency to the user. Also most preferably, such an architecture is extensible, allowing easy insertion to and removal from the SAN of hosts, storage drive arrays or subsystems, and any appliances that are introduced into the SAN to form part of that architecture.